Logical Domains

Logical Domains (LDoms or LDOM) is the server virtualization and partitioning technology from Sun Microsystems released in April 2007. It has been re-branded as Oracle VM Server for SPARC since Oracle Corporation completed the acquisition of Sun in January 2010. ^[1]

Each domain is a full virtual machine with a reconfigurable subset of hardware resources. Operating systems running inside Logical Domains can be started, stopped, and rebooted independently.

Supported hardware

The SPARC Hypervisor runs in the Hyper-Privileged execution mode, which was introduced in the sun4v architecture. The sun4v processors released as of September 2010 are the UltraSPARC T1, the UltraSPARC T2, the UltraSPARC T2 Plus and the SPARC T3 ^[2]. Only systems based on those processors support Logical Domains. These include the UltraSPARC T1-based:

• Sun / Fujitsu SPARC Enterprise T1000 and T2000 servers
• Sun Fire T1000 and T2000 servers
• Netra T2000 Server
• Netra CP3060 Blade
• Sun Blade T6300 Server Module

UltraSPARC T2-based:

• Sun / Fujitsu SPARC Enterprise T5120 and T5220 servers
• Sun Blade T6320 Server Module
• Netra CP3260 Blade
• Netra T5220 Rackmount Server

UltraSPARC T2 Plus systems:

• Sun / Fujitsu SPARC Enterprise T5140 and T5240 servers (2 sockets)
• Sun Blade T6340 Server Module (2 sockets)
• Sun / Fujitsu SPARC Enterprise T5440 (4 sockets)

And SPARC T3 systems ^[3]:

• Sun / Fujitsu SPARC T3-1 servers (1 socket)
• Sun SPARC T3-1B Server Module (1 socket)
• Sun / Fujitsu SPARC T3-2 servers (2 sockets)
• Sun / Fujitsu SPARC T3-4 servers (4 sockets)

Logical Domains exploits the "Chip Multi Threading" (CMT) nature of the UltraSPARC T1, T2, and SPARC T3 processors. A single chip contains up to 16 CPU cores, and each core has either four hardware threads (for the T1) or eight hardware threads (for the T2, T2+ and T3) that act as virtual CPUs. All CPU cores execute instructions concurrently, and each core switches between threads—typically when a thread stalls on a cache miss or goes idle—within a single clock cycle. This lets the processor gain throughput that is lost during cache misses in conventional CPU designs.

Each processor can support as many as one domain per hardware thread—up to 32 domains for the UltraSPARC T1, 64 domains for the UltraSPARC T2, and 128 domains for UltraSPARC T2+ servers with two physical processors or any number of SPARC T3 processors^[4]. Alternatively, and in usual practice, a given domain can be assigned multiple CPU threads for additional capacity within a single OS instance. CPU threads and virtual I/O devices can be added to or removed from a domain by administrator command in the control domain. This change takes effect immediately without needing to reboot the affected domain, which can immediately make use of added CPU threads or continue operating with reduced CPU threads.

Logical Domain roles

All logical domains are the same except for the roles that you specify for them. There are multiple roles that logical domains can perform such as:

• Control domain
• Service domain
• I/O domain
• Guest domain

The Control domain, as its name implies, controls the logical domain environment. It is used to configure machine resources and guest domains, and provides services necessary for domain operation, such as virtual console service. The control domain also normally acts as a service domain.

Service domains present virtual services, such as virtual disk drives and network switches, to other domains. In most cases, guest domains perform I/O via bridged access through services domains, which are directly connected to the physical devices. Service domains can provide virtual LANs and SANs as well as bridge through to physical devices. Disk images can reside on complete physical disks, slices (partitions of a disk), or even on files contained on a UFS or ZFS filesystem. Current processors can have two service domains in order to provide resiliency against failures.

I/O domain has direct ownership of and direct access to physical I/O devices, such as a network card in a PCI controller. It shares the devices to other domains in the form of virtual devices. You can have a maximum of two I/O domains for the UltraSPARC T1 (Niagara) servers, one of which also must be the control domain. UltraSPARC T2 Plus and SPARC T3 servers can have as many as 4 I/O domains.

Guest domains run an operating system instance without performing any of the above roles, but leverage the services provided by the above in order to run applications.

Control and service functions can be combined within domains, however it is recommended that user applications not run within control or service domains in order to protect domain stability and performance.

Supported guest operating systems

• Solaris 10 11/06 or later
• OpenSolaris 2009.06 release
• Ubuntu Linux Server Edition
• FreeBSD (under development)^[5]
• OpenBSD 4.5 or later^[6]
• Wind River Platform for Network Equipment, Linux Edition (announced availability: second half of 2007)^[7]

References

1. ^ "Oracle + Sun: Transforming the IT Industry". Oracle Corp. http://www.oracle.com/us/sun/044498.html. Retrieved 2010-01-27. 
2. ^ "Oracle Unveils SPARC T3 Processor and SPARC T3 Systems". http://www.oracle.com/us/corporate/press/173536. Retrieved 2010-09-20. "Using the newly announced Oracle VM Server for SPARC 2.0, the SPARC T3 systems offer advanced virtualization and have multiple virtual machines ranging from one per core to 128 virtual machines on a single server, delivering greater efficiencies and lower costs through consolidation." 
3. ^ "Oracle Unveils SPARC T3 Processor and SPARC T3 Systems". http://www.oracle.com/us/products/servers-storage/servers/sparc-enterprise/t-series/index.html. Retrieved 2010-09-20. "Sun SPARC Enterprise T-Series RackMount Systems New! SPARC T3-1 Server New! SPARC T3-2 Server New! SPARC T3-4 Server" 
4. ^ "Oracle Unveils SPARC T3 Processor and SPARC T3 Systems". http://www.oracle.com/us/corporate/press/173482. Retrieved 2010-09-20. "Oracle VM Server for SPARC (previously called Logical Domains) is a server virtualization solution that allows up to 128 virtual servers on one system ." 
5. ^ "FreeBSD/sun4v Project". The FreeBSD Project. http://www.freebsd.org/platforms/sun4v.html. Retrieved 2007-05-02. 
6. ^ "Support for Logical Domains on Sun's CoolThreads servers". OpenBSD Journal. http://undeadly.org/cgi?action=article&sid=20090201164147. Retrieved 2009-03-19. 
7. ^ "Wind River To Support Sun's Breakthrough UltraSPARC T1 Multithreaded Next-Generation Processor" (Press release). Wind River Systems, Inc.. November 1, 2006. http://www.windriver.com/news/press/pr.html?ID=3881. Retrieved 2007-05-02. 

See also

• Oracle VM

External links

• Virtualization Solutions from Oracle
• Logical Domains at Sun.COM
• Logical Domain Manager Software at Fujitsu
• Logical Domains at BigAdmin System Administration Portal
• Sun BluePrint: Beginners Guide to LDoms: Understanding and Deploying Logical Domains
• Sun BluePrint: Energy Efficiency Strategies: Sun Server Virtualization Technology
• Sun BluePrint: Using Logical Domains and CoolThreads Technology: Improving Scalability and System Utilization
• Sun Virtualization Solutions
• Logical Domains Community at OpenSolaris.org
• Libvirt for LDoms, see documentation
• Logical Domains (LDoms) - presented at the OpenSolaris usergroup meeting